Estimating Sampling Errors in REA Survey: A Model Approach for the Synthetic Presentation of Results for Main Variables Involved in Economic Analysis

A new sample business survey for agriculture, the REA survey, and a project of integration with the FADN network (RICA in Italy) have significantly changed the production of statistical information nowadays available with reference to the agricultural sector. On the basis of this relevant information, new economic analyses are being developed on farms’ performance, agricultural households’ income and the Common Agricultural Policy (CAP). In this paper the authors estimate the relationship between the levels of variables of interest and their sampling errors using models in order to improve the accessibility of the information on estimates accuracy to the final users (agricultural analysts, policy makers). The paper is the result of a joint research of the three authors. Sections 1–3 and 6 by Pizzoli, Sects. 4 and 5 by Rondinelli, Sect. 7 by Filiberti, conclusions joint to the three authors.     

Separable subgroups of mapping class groups

We investigate separability questions for the mapping class group of a surface. While this group is not subgroup separable in general, we prove a large family of interesting subgroups are separable. This includes many classically studied subgroups such as solvable subgroups, Heegaard and Handlebody groups, geometric subgroups, and all the terms in the Johnson filtration.     

Nonminimal sets,their projections and integral representations of stable processes

New criteria are provided for determining whether an integral representation of a stable process is minimal. These criteria are based on various nonminimal sets and their projections, and have several advantages over and shed light on already available criteria. In particular, they naturally lead from a nonminimal representation to the one which is minimal. Several known examples are considered to illustrate the main results. The general approach is also adapted to show that the so-called mixed moving averages have a minimal integral representation of the mixed moving average type.     

Magnetic phases in Mn<Subscript>1</Subscript>_<Subscript>x</Subscript>Fe<Subscript>x</Subscript>WO<Subscript>4</Subscript> studied by neutron powder diffraction

The magnetic structures of Mn_1-xFe_xWO₄ with x = 0.0, 0.16, 0.21, 0.225, 0.232, 0.24, 0.27, 0.29, and 1.0 were refined from neutron powder diffraction data. The magnetic phase diagram could be completed in the coexistence range of different magnetic structures up to x = 0.29. For the magnetic state at 1.5 K a commensurate antiferromagnetic structure with a propagation vector = (±1/4, 1/2, 1/2) was found for x ⩽ 0.22 while the magnetic spins order with = (1/2, 0, 0) for x ≥ 0.22. In the latter phase, additionally, weak magnetic reflections indexed to an incommensurate ordering with = (- 0.214, 1/2, 0.457) occur in the diffraction pattern up to x = 0.29 indicating the occurence of a reentrant phase. For 0.12 ⩽ x ⩽ 0.29 the low temperature phases are separated from a magnetic high temperature phase showing only magnetic reflections indexed to a spin arrangement with = (1/2, 0, 0). The magnetic phase diagram is discussed qualitatively considering random superexchange between the statistically distributed Mn²⁺- and Fe²⁺-ions in the coexistence range 0.12 ⩽ x ⩽ 0.29 of different magnetic structures related to those of pure MnWO₄ and FeWO₄. Received 9 October 2002 Published online 14 March 2003     

Arithmetic expressions of Selberg's zeta functions for congruence subgroups

In [P. Sarnak, Class numbers of indefinite binary quadratic forms, J. Number Theory 15 (1982) 229-247], it was proved that the Selberg zeta function for SL₂(Z) is expressed in terms of the fundamental units and the class numbers of the primitive indefinite binary quadratic forms. The aim of this paper is to obtain similar arithmetic expressions of the logarithmic derivatives of the Selberg zeta functions for congruence subgroups of SL₂(Z). As applications, we study the Brun-Titchmarsh type prime geodesic theorem and the asymptotic formula of the sum of the class number.     

Ionic conductivity of epitactic MBE-grown BaF2 films

We studied parallel conductivities of pure BaF₂ films with thicknesses ranging from 35 to 300 nm, epitaxially grown on Al₂O₃(0 1 2) substrates by molecular beam epitaxy technique. The overall conductivities of the films are found to increase with decreasing thickness. The detailed investigation of the overall conductance as a function of the thickness permits the deconvolution of bulk and boundary effects, the latter being attributed to distinct space charge effects in the interface between BaF₂ film and Al₂O₃ substrate. The (extrinsic) Debye length (λ) is estimated to be about 8 nm at T=593 K, which corresponds to an impurity content of 10¹⁸/cm³ (singly ionized dopant assumed). This is consistent with the fact that we observed a constant boundary contribution for all investigated films (film thickness >4λ). It is also consistent with the Debye length observed in a previous report on CaF₂/BaF₂ heterolayers fabricated by the same technique, in which the low temperature enhancement was also attributed to space charges in BaF₂ [Nature 408 (2000) 946]. Only at low temperatures (below 370 °C), the conductance seems to be influenced by strain effect.     

Organic synthesis based on cathodic deprotonation of acids

The results of studies on electrosynthesis involving carb- and heteroanions generated by cathodic deprotonation of acids (CDA), carried out in the laboratory headed by the author, are surveyed. These studies resulted in the elaboration of efficient electrochemical versions of the known Michaelis-Becker, Wittig-Horner, and Perkin reactions; electrochemical analogs of homolytic aromatic substitution, alkylation, heterocyclization,etc. were developed. Based on CDA, convenient and promising methods for preparing variousN-, O-, P-, S-, andC-alkylated and arylated substances have been developed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1411–1422, August, 1995.The author is grateful to Professor V. A. Dorokhov, Professor V. P. Litvinov, and researchers from the laboratories of N. D. Zelinsky Institute of Organic Chemistry headed by them, who participated in joint studies.The work was carried out with financial support from the International Science Foundation (Grant No. MHYOO).     

Global stability and periodic solution of the viral dynamics

It is well known that the mathematical models provide very important information for the research of human immunodeficiency virus-type 1 and hepatitis C virus (HCV). However, the infection rate of almost all mathematical models is linear. The linearity shows the simple interaction between the T cells and the viral particles. In this paper, we consider the classical mathematical model with saturation response of the infection rate. By stability analysis we obtain sufficient conditions on the parameters for the global stability of the infected steady state and the infection-free steady state. We also obtain the conditions for the existence of an orbitally asymptotically stable periodic solution. Numerical simulations are presented to illustrate the results.     

First-principles study of indium on silicon (1 0 0)—the structure, defects and interdiffusion

The atomic structures of indium (In) on silicon (Si) (1 0 0)-(2 × 1) surface are investigated by the local density approximation using first-principles pseudopotentials. Total energy optimizations show that the energetically favored structure is the parallel ad-dimer model. The adsorption energy of In on ideal Si(1 0 0)-(1 × 1) surface is significantly higher than that on reconstructed Si(1 0 0)-(2 × 1) surface, suggesting that In adsorption does not break the Si-Si dimer bond of the substrate. When Si surface contains single dimer vacancy defects, In chain will be interrupted, leading to disconnected In nanowires. Displacive adsorption of In on Si(1 0 0) is also considered, and the calculation suggests that interdiffusion of In into Si substrate will not be favorable under equilibrium conditions.